An aggressive, powerful scrum-half, Phillips made his international debut in 2003 against Romania while understudy to Dwayne Peel at Llanelli Scarlets.

His early international career was also spent in the shadow of Peel, with first team opportunities limited until injury ruled his rivall out of the 2005 clash with the All Blacks at the Millennium Stadium. Phillips' big chance proved to be a false start, as he turned in a stuttering performance in a heavy 41-3 defeat. Earlier in the year Phillips had made the switch to Cardiff Blues from Llanelli, and was in fine form at club level.

Despite his poor performance in the Autumn Internationals, Phillips was selected as cover for Peel during the 2006 Six Nations. Following and injury to Peel against Italy, Phillips put in a Man of the Match performance against France at the Millennium Stadium. Showing the devastating running lines and power that his 6'3" frame can bring to the international game, Phillips decimated the French defence and finally showed the form that he had been in at domestic level.

The return of Peel for the Autumn Internationals in 2006 meant that Phillips was again relegated to the bench for the 2007 Six Nations. At the start of the 2006/7 season Phillips had made a high profile move to the big spending Ospreys, with his contract rumoured to be worth £180,000 a year.

His competition with Justin Marshall at club level translated to the international arena, as he continued to scrap with Peel for the 9 jersey. Phillips was selected in Gareth Jenkins' squad for the World Cup in 2007, but again found his opportunities limited to those from the replacements bench despite wavering form from Peel.

Phillips' fortunes would change under the new Wales coaching setup, with Warren Gatland selecting him for the 2008 Six Nations opener against England. Phillips scored the decisive try following his own charge down, and remained first choice scrum half for the rest of the tournament.

His performances marked him out as one of the players of the tournament and also as a potential Lions tourist in 2009. Phillips was unable to travel on Wales' summer tour to South Africa after sustaining a tear to his anterior cruciate ligament and a grade-two tear to the medial collateral ligament in the Ospreys' Anglo-Welsh Cup semi-final win over Saracens.

Phillips recovered from injury to play a part in Wales' unsuccessful Six Nations defence and was selected for the 2009 Lions tour of South Africa. He won selection for all three Tests and capped a fine display in the first match with the Lions' third try. Even though the Lions went down 2-1 in the series, Phillips was widely regarded as one of the Lions' best players on tour. Following his return Phillips found himself in trouble with the law after an altercation with a taxi driver, an incident that lead Wales coach Neil Jenkins to warn him over his future in the international setup.

An ankle injury ruled out any participation in Wales' November series but he was rushed back for a spot on the replacements bench as they took on France in February 2010. He was an unused option, with Richie Rees making his full debut to good effect. Soon after he signed a new four-year deal with the Ospreys and helped his region to the Magners League title with victory over Leinster in May.

Phillips regained his international place for the summer tour to New Zealand but again came under increasing pressure from Rees during the 2010 November internationals after a sluggish start to the season. He continued to struggle to reach his top form in the early games of the 2011 Six Nations but scored a crucial, if controversial, try as Wales beat Ireland to move into second in the Championship table.

At the end of the tournament it was confirmed, by coach Scott Johnson, that he would be leaving the Ospreys at the end of the 2010-11 season, with France initially presumed to be his most likely destination. Despite rumours he was entertaining the idea of switching codes to the Celtic Crusaders, Top 14 outfit Bayonne announced his signature in June 2011. But his World Cup hopes were dealt a huge blow the same week when he was suspended indefinitely from Wales duties in the wake of an alleged late-night incident in Cardiff city centre whilst on an agreed holiday period from pre-Rugby World Cup training.

Phillips started all seven of Wales' 2011 World Cup matches and scored tries against Ireland in the quarter-finals and against France in the semi-finals. He was powerless to prevent Wales from being knocked out but continued to play a key part in the Wales side despite plying his trade in France for Bayonne.

Phillips played in all five of Wales' 2012 Six Nations matches and helped guide them to their famous Grand Slam. His form came under scrutiny as Wales slumped to eight successive defeats. But they overhauled that run to retain the Six Nations title in 2013, with Phillips at the heart of their effort.

Phillips was then named in Warren Gatland's 37-man Lions squad to tour Australia. He began the tour with a bang with a great performance against the Barbarians in Hong Kong and was always in pole position to start the first Test. A laboured performance against opposite number Will Genia, and a troublesome knee, saw him dropped for the second Test against the Wallabies. But he returned to the starting line-up for the final Test in Sydney and helped the Lions secure a 2-1 series victory over Australia.